Enzymes

Enzymes are biological catalysts that speed up chemical reactions without being used up.

They work on specific molecules (substrates) using a "lock and key" model:

Optimum Conditions:

Temperature:
- Low temperature slows reactions (enzymes and substrates move slower).
- High temperature denatures enzymes (active site changes shape, stopping function).
pH:
- Too high or too low pH denatures enzymes, stopping them from working.

The lock and key model of enzyme action

Prepare the Solutions:

Prepare the Enzyme and Starch Solutions:

Add 5 cm³ of starch solution and 5 cm³ of amylase solution to separate test tubes.
Place these test tubes in the same water bath.

Wait and Set Up:

Start the Reaction:

Add 1 cm³ of starch solution and 1 cm³ of amylase solution to the test tube containing the pH 3 buffer.
Start a timer.

Test for Starch:

After 30 seconds, remove a small sample from the test tube with a pipette.
Add this sample to a well in the spotting tile containing iodine solution.
Observe the color:
- Black: Starch is still present.
- No color change: Starch has been broken down.
Return any unused solution to the water bath.
Repeat Sampling:
- Continue testing every 30 seconds until the iodine no longer turns black.
- Record the time when this happens.
Repeat for All pH Buffers:
- Perform the experiment with buffer solutions at pH 5, 7, 9, and 11.
- If the iodine still turns black after 10 minutes, record “no change after 10 minutes.”

Typical results for an amylase enzyme test

Calculating the Rate of Reaction:

Use these formulas:
- Rate = substrate used / time
- Rate = product formed / time
Measurements:
- Substrate or product: Grams (g) or centimeters cubed (cm³).
- Time: Seconds (s) (convert from minutes if necessary).
Units for rate: g/s or cm³/s.

Determine the Optimum pH:

The pH with the fastest rate of reaction is closest to the enzyme's optimum.
The actual optimum pH likely lies between the two pH levels with the fastest rates (e.g., between pH 7 and 9).